The 15KM ultra-long-distance wifi module manufacturer explained the classification of wireless communication transmission models. In the network planning stage and network optimization period, the most important communication problem is path loss, which represents the characteristics of large-scale communication and has the communication characteristics of strong laws. Path loss is an important basis for the planning and design of mobile communication systems, and affects the coverage, signal-to-noise ratio and distance effects of cellular design. Therefore, in the initial planning stage of a mobile communication network, or future expansion, path loss needs to be predicted during network optimization. The wireless communication model is used to predict the path loss in different communication environments, so as to better build the local wireless communication network.
The radio signal sent by the base station not only has the path loss encountered in the communication in the atmosphere, but also is affected by the ground communication path loss, and the ground communication loss is greatly affected by the terrain objects. Mobile platforms have low antenna heights, usually very close to the ground plane, which is one reason for this additional communication loss. Generally speaking, the texture and roughness of the ground tends to cause energy consumption and reduce the received signal strength of mobile platforms and base stations. This type of loss, combined with the free space loss, together constitutes the communication path loss.
Mobile radio signals are also affected by various multi-diameter phenomena - they can cause severe signal fading, and these effects come from the mobile radio communication medium. The fading of mobile radio signals includes long-term fading and short-term fading, which is a statistical classification. Long-term fading is usually caused by small-scale topographical changes along the propagation path. Short-term fading is usually caused by stationary and moving reflections from various signal diffusers. This fading is called multi-diameter fading.
Accurately describing changes in transmitted signals in such a complex environment is a very difficult task. The following model predicts changes in wireless signals through extensive measurement data or precise electromagnetic theoretical calculations.
In the design of mobile communication network, one of the main tasks is to make the network achieve satisfactory quality coverage, voice quality, voice loss rate and connection rate under the condition of voice capacity that meets the needs of mobile users. A large part of it has to do with the quality of the received signal, which is mainly determined by the communication conditions between transmit and receive. In analyzing the radio wave transmission process of mobile communication, the communication path loss is one of the main parameters that people pay attention to. 15KM ultra-long-distance wifi module manufacturers can use the wireless communication model analysis method to predict the communication path loss of radio waves.
According to the nature of the wireless propagation model, it can be divided into the following categories:
(1) Empirical model.
(2) Semi-empirical or semi-deterministic models.
(3) Deterministic model.
An empirical model is a formula derived from statistical analysis based on a large number of test results. The method of predicting the path loss with an empirical model is very simple and does not require accurate information about the relevant environment, but does not provide a very accurate estimate of the path loss. The deterministic model is the direct application of electromagnetic theoretical calculation methods to a specific field environment. The environment description can be obtained from a terrain database, and different levels of accuracy can be found in the environment description. In deterministic models, several techniques are used, usually based on ray tracing methods: geometric diffraction theory, physical optics, and less commonly used precise methods such as integral equation methods or finite difference time domain methods. Deterministic wireless transmission prediction is an extremely complex electromagnetic problem in urban, mountainous and indoor environments. Semi-empirical or semi-deterministic models are equations derived using deterministic methods in general urban or indoor environments. Sometimes, in order to improve its agreement with the experimental results, the equations are modified from the experimental results as a function of specific features around the antenna.
Due to the diversity of mobile communication environments, each communication model is designed for a specific type of environment. Therefore, 15KM ultra-long-distance wifi module manufacturers can be classified according to the application environment of the communication model. Three types of environmental communities are generally considered: macrocells, macrocells, microcells or microcells, and microcells or microcells.
(1) Macro cell
The macro cell has a large area, covering a large area with a radius of about 1~30km. Base station transmit antennas are usually located above surrounding buildings. Usually, there are direct rays.
(2). Micro cell
The coverage radius of a micro cell is between 0.1 and 1 km, and the coverage area is not necessarily a circle. The height of the transmitting antenna can be the same as the height of the surrounding buildings or slightly higher or lower. Generally, it is divided into two categories according to the relative positions of the transceiver antenna and the environmental obstacles: LOS line-of-sight and NLOS non-line-of-sight.
(3) Pico cell
The typical radius of a picocell is between 0.01 and 0.1 km. Pico cells can be divided into two categories: indoor and outdoor. The transmitting antenna is under the roof or inside the building. LOS and NLOS should generally be considered separately, whether indoors or outdoors.
In general, there is an adaptive relationship between the three models and the three community types. For example, the experiential model and the semi-experience model are suitable for macro cells with uniform characteristics, and the semi-experience formula is also suitable for uniform micro cells. The parameters considered by the model are a good representation of the entire environment. Deterministic models apply to both micro and micro cells. Regardless of their shape, they are not suitable for macro cells because the CPU time required for such an environment makes these techniques inefficient.
Macro cell propagation mode
The Okumura-Hata model is a formula fitted by Hata on the basis of a large number of test data in Okumura. Since the Okumura model is used, the various curves it gives need to be found, which is not good for computer predictions. Based on Okumura's basic median field strength prediction curve, Hata proposes an empirical formula for communication loss, the Okumura-Hata model.
In order to simplify this model, 15KM ultra-long-distance wifi module manufacturers made the following three assumptions:
(1). Treated as the propagation loss between two omnidirectional antennas;
(2). Treat as quasi-smooth terrain rather than irregular terrain;
(3). The urban propagation loss formula is used as the standard, and the correction formula is used in other areas for correction.
Applicable conditions:
(1) f is 150~1500mHz;
(2) The effective height hb of the base station antenna is 30~200 meters;
(3) The antenna height hm of the mobile station is 1~10 meters;
(4). The communication distance is 1~35km;
Formula description:
The unit of d is km;
f is in MHz;
LB city is the median of the city's basic transmission loss;
HB, hm-base station, the effective height of the mobile station antenna, the unit is meters;
Calculation of the effective height of the base station antenna: the height of the base station antenna is hs, the height of the base station is hg, the height of the mobile station antenna is hm, the height of the mobile station is hmg, the effective height of the base station antenna is hb=hs+hg-hmg, The effective height of the mobile station antenna is hm. Note: There are many ways to calculate the effective height of the base station antenna, such as the average level of the ground altitude within 5~10 kilometers around the base station; the terrain fitting line of the ground altitude within 5~10 kilometers around the base station; etc.; different The calculation method is related on the one hand to the communication model used and the calculation accuracy requirements.
The COST-231-Hata model is also a formula obtained by analyzing the high-frequency Okumura propagation curve based on the test results of Okumura et al.
Applicable conditions:
(1).f is 1500~2000mHz;
(2) The effective height hb of the base station antenna is 30~200 meters;
(3) The antenna height hm of the mobile station is 1~10 meters;
(4). The communication distance is 1~35km.
Propagation loss formula: Propagation loss formula:
The unit of d is km, and the unit of f is MHz;
LB city is the median of the city's basic transmission loss;
HB, hm-base station, the effective height of the mobile station antenna, the unit is meters;
Calculation of the effective height of the base station antenna: the height of the base station antenna from the ground is hs, the height of the base station is hg, the height of the mobile station antenna is hm, and the height of the mobile station is hmg. The effective height of the base station antenna is hb=hs+hg-hmg, and the effective height of the mobile station antenna is hm.
microcell propagation mode
The two-ray transport model only considers the contributions of direct rays and ground-reflected rays. It is suitable for flat rural environments and also for microcell communities where base station antennas are low because there are LOS paths between the transmit and receive antennas. In this case, if the walls of the building also reflect and bypass the waves, they will cause rapid changes in the field strength in the simple two-ray model, but will not change the value of the overall path loss power law exponent n predicted by the two-ray . The path loss given by the two-ray mode is written as a function of the distance d between the transceiver and the transceiver, which can be analogous to two straight line segments with different slopes n1 and n2. The abrupt point between two line segments is also called the distance of the inflection point between the emitters:
hr and ht are the heights of the transmit and receive antennas, respectively.
Path loss can be consumed by:
This approximation is called a double slope model. Theoretically, the n1 and n2 values for the two-ray ground reflection model are 2 and 4, respectively. The measurement results of 1800~1900mHz in the urban microcellular community show that the value of n1 is between 2.0 and 2.3, and the value of n2 is between 3.3 and 13.3.
The multi-ray model has been used in urban microcellular communities under LOS conditions, when the transmit and receive antennas are well below the roof plane. These models assume that the so-called street-medium canyon structure also becomes a waveguide structure, the site at the receiving end, from direct rays between receive and transmit, reflections along the ground, and the vertical plane building walls of the canyon. The two-ray model can be viewed as a multi-ray model that considers only two rays. Four-ray and six-ray models are proposed: the four-ray model consists of direct rays, ground-reflected rays, and two types of rays reflected by the building walls; the six-ray model and the four-ray model have the same mechanism, and both are reflected twice by the building.
When the multi-ray model is used in an urban environment, the 15KM ultra-long-distance wifi module manufacturers usually assume that the street buildings are arranged in a row, and there is no gap between the buildings. Blaunstein and Levin proposed a multi-gap waveguide structure model, taking into account the actual dielectric properties of the building walls, the actual distribution of street widths and reflections from the road are shown in Figure 1. The model assumes that the urban fabric is formed by gaps between two parallel rows of randomly spaced buildings. Consider the direct site, reflections from building walls, corners and ground reflections.
Indoor propagation mode.
Experimental studies point out that the propagation path NLOS of obstacles in buildings will experience Rayleigh fading, while the line-of-sight path LOS is independent of the building type. Rice fading consists of strong line-of-sight LOS paths and many weakly reflective ground paths. Building materials, aspect ratios of building edges, and window types suggest that they have an effect on RF attenuation between floors. Measurements show that the loss between floors does not increase linearly with separation distance. For the first layer, the typical value of attenuation between floors is 15dB, and then each layer increases by 6~10dB, divided into 4 layers at most. For 5 or more layers of separation, the path loss per layer only increases by a few decibels.
For the indoor system covered by the outdoor base station, the experimental research of the 15KM ultra-long-distance wifi module manufacturer shows that the signal strength received inside the building increases with the height of the floor. On the lower floors of the building, the signal level penetrating into the building is small due to the large attenuation of the urban agglomeration. In higher floors, if there is a line-of-sight path, a strong direct signal to the building's exterior walls is generated. The penetration loss of the signal is a function of frequency and height inside the building. Penetration loss increases with frequency. Measurements have shown that windows have 6db less penetration loss than buildings without windows.
Logarithmic Distance Path Loss Model
L50(d) is the average path loss db, d is the distance m between sending and receiving, l(d0) is the path loss from the transmitting point to the reference distance d0, d0 is the reference distance m, n depends on the average path loss index of the environment . The reference path loss can be calculated from the test or free space path loss representation.
The path loss found from above is log-normally distributed. The mean path loss exponent n and standard deviation depend on the parameters of building type, building side, number of floors between transmitter and receiver. The path loss for a receive interval of D meters can be given by:
(d)=L50(d)+X)
This is an experience model, where X—is a standard deviation (DB) zero-mean log-normally distributed random variable representing the effect of environmental features.
Attenuation factor model
In type, n1 is the path loss index at the same floor. This depends on the type of building, with a typical value of 2.8; FAF is the floor attenuation factor, a function of the number of floors and building type. The application of 15KM ultra-long-distance wifi module manufacturer's propagation model in cellular design. In wireless cellular design, to predict the coverage radius or receive power link budget of the receiver, the following formula can be used:
Pr=Pt+GT+Gr-Lt-Lr-Lbf. In the formula, Pr and PT receive power and transmit power, respectively, and the unit is DBM; GR and GT are the gain of the transceiver antenna, and the unit is DB; LR and LT are the feeder loss of the uplink and downlink, and the unit is DB; LBF is the transmission path loss, in DB. LBF can be predicted by the above model.
In order to improve the prediction accuracy and reduce the workload of wireless network planning engineers, more computer programs are used to predict the transmission loss and the area covered. The prediction of path loss is closely related to the terrain, terrain and distance around the base station, so we can store the terrain, terrain and other information in the electronic map, which can be recalled by the computer at any time.
